1. Field of the Invention
This invention relates to orthopedic devices for individuals whose bones have been weakened by injury and support and stabilization of the bones is necessary. In particular, the present invention relates to a suspension strap for a knee orthosis that provides optimum support and suspension by maximizing the contact area between the orthosis and the wearer's body.
2. Description of Related Art
A conventional orthopedic knee brace is shown in U.S. Pat. No. 5,415,625 to Cassford et at. The knee brace includes rigid upper and lower cross members, and includes upper and lower medial and lateral arms (or struts) that are connected by hinges, thereby permitting pivotal movement of the knee. In addition, attachment straps are used to secure the brace to the leg of the user together with cross members running between the lateral and medial struts. It should be noted that while Cassford et al. appears to disclose an "off-the-shelf" type of a knee brace, where the support elements are not formed to fit a particular user's leg, conventional knee braces may also be of a custom made design, where shell-type support members are molded to conform to the shape of the specific wearer's leg.
The Cassford et al. design provides inflatable pads mounted on the struts for adjusting the fit of the brace to a particular user or for a particular activity. The inflatable pads, however, suffer from the problem that one must continuously monitor the pads and inflate/deflate them as necessary using independent fluid injecting devices. In addition, the inflatable pads can cause an offset of the intended contact area between the attachment straps and the person's leg, which may lead to unsatisfactory support from the attachment straps. In extreme situations, this problem may cause unintended areas of the person's leg to be compressed, resulting in dangerous pressure on nerves in the leg.
The attachment straps in the Cassford et al. design are positioned in a conventional fashion, traversing on the outside of the orthosis from the medial to lateral struts, with attachment points on the outside of the struts or shells. This positioning of the attachment straps, however, has drawbacks. By having the attachment points on the outside of the strut or shell, a decreased surface area of the attachment strap contacts the wearer's skin which, in turn, decreases the amount of direct support provided by the straps, particularly the calf suspension strap. In addition to this decreased area of support, having the attachment straps attached in this fashion causes an inward tightening of the brace in a medial-lateral fashion. This tightening is disadvantageous because it results in the hinge pads being unduly forced against the knee joint. In addition, the tightening may cause the struts to be misangled relative to the person's leg.
U.S. Pat. No. 4,633,867 to Kausek et al. discloses a knee brace that includes a flexible, elastic popliteal strap that extends in a substantially horizontal plane around the back of the upper calf. The popliteal strap, however, is only used for compressing a shin plate against the leg and prohibits excessive rotation or misalignment of the shin plate. The popliteal strap is elastic and flexible, and therefore does not provide any firm support or stabilization of the knee that a calf suspension strap provides. In addition, this strap attaches to the outside of the shin plate or shell, and therefore it does not provide the maximum contact area possible between the strap and the wearer's body. Furthermore, having the strap aligned in a horizontal fashion, perpendicular to the wearer's leg, results in the possible risk that the strap is directed towards the critical area of a peroneal nerve which is located at the neck of the fibula. The strap's line of action is directly over the neck of the fibula, creating a distinct risk of compressing the peroneal nerve. It should be noted that the conventional attachment of the attachment straps, as disclosed in Cassford et al., avoided this problem of placing pressure on the peroneal nerve by attaching the attachment straps on the outside of the orthosis shell. Such designs avoid pressure on the nerve because the calf strap does not place pressure on the fibular neck, an area where the nerve crosses close to the surface of the skin. However, in the Cassford et al. design, this advantage may be negated due to the inflatable pads causing a repositioning of the attachment straps, as discussed above.
Other conventional designs for knee braces are disclosed in U.S. Pat. No. 5,092,030 to Maurer, U.S. Pat. No. 4,732,143 to Kausek et al., and U.S. Pat. No. 4,312,335 to Daniell, Jr. The above-discussed problems with the prior art indicate that the need exists for a knee orthosis in which maximum contact area between the calf suspension strap and the wearer's leg can be obtained without the risk of damaging nerves in the leg.